CyberDruid

Is a PSU a critical factor in acheiving a stable overclock?

In short yes it is.

It is not simply the amperage or the wattage either. Having built a number of rigs strictly for OCing I have found that even a PSU that is rated well above the calculated power requirements may fail to provide a stable overclock. Why? In part it is the minute fluctuations in the current to the mobo. While it is easy to spot a sagging rail with monitoring SW or a multimeter it requires much more sophisticated equipment to see the wave form activity on the rails. In a recent PSU torture test at Tom's Hardware Guide the testers reported on just that factor. Spikes in the voltage (ripple) induced by the PFC circuitry and/or construction of the transformer vary a great deal from make to make. When running at the edge with a high overclock such effects become a major hindrance to stability. This only becomes more pronounced when the PSU approaches maximum load and the circuitry trying to maintain the specific voltage is being stressed by temperature and system demands.

Clean power is not something you will be able to monitor or detect with SW like Everest or MBM5--but it's effects are apparent. A well built PSU will feature one or more methods of maintaining the desired voltage regardless of draw. Not all PSUs are equal in that aspect. It is a truism that you get what you pay for RE: PSUs--the heavier the better too! By sticking to known performers from reputable manufacturers you can increase your chance of a successful ovecclock.

Stable power can mean being able to turn down the Vcore a notch too! I learned that from upgrading and swapping around PSUs on the Folding Farm--with the more inexpensive/no name PSUs I needed to really crank up the Vcore for stability when at maximum OverClock--after upgrading to Server-quality PSUs I was able to lower my Vcore considerably. In a few instances i was able to go lower than spec for cooling purposes without reducing stability.

It is not so much a matter of getting a bigger (more powerful) PSU as it is getting a "real" PSU that can provide clean power. For instance, a 350 watt Enermax with a 26A +12v rail is going to perform better when under maximum load than a Mad Dog 450 watt with an 18A +12V rail at partial load.

Although a certain variance can be expected--the closer a PSU keeps all the rails to specification the better your components will perform, with fewer instabilities. The PSU is not the place to save a few dollars if you are hoping to overclock to the limit. Considering the life span of a good PSU it is likely that by choosing the very best you can afford now, you won't have to upgrade it later on when upgrading other components thereby saving money. Hope this helps explain why an excellent 350 watt PSU can out perform a so-so 500 watt PSU when pushing your system to the limit.

Good Luck and Good Overclocking!

CyberDruid

Chozart

The 'Druid strikes again! Great little FAQ :) Another rep for you (ok, just one... just one)

CyberDruid

You are very kind oh Master of PSU lore...I hope to flesh this out with more technical data soon!